Respirators are commonly worn over the breathing passages of a person for at least one of two common purposes: (1) to prevent impurities or contaminants from entering the wearer's breathing track; and (2) to protect other persons or things from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains particles that are harmful to the wearer, for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is risk of contamination to other persons or things, for example, in an operating room or clean room.
Some respirators are categorized as being “filtering face-pieces” because the mask body itself functions as the filtering mechanism. Unlike respirators that use rubber or elastomeric mask bodies in conjunction with attachable filter cartridges (see, e.g., U.S. Pat. No. RE39,493 to Yuschak et al.) or insert-molded filter elements (see, e.g., U.S. Pat. No. 4,790,306 to Braun), filtering face-piece respirators have the filter media comprise much of the whole mask body so that there is no need for installing or replacing a filter cartridge. As such, filtering face-piece respirators are relatively light in weight and easy to use. Examples of patents that disclose filtering face-piece respirators include U.S. Pat. No. 7,131,442 to Kronzer et al, U.S. Pat. Nos. 6,923,182 and 6,041,782 to Angadjivand et al. U.S. Pat. Nos. 6,568,392 and 6,484,722 to Bostock et al., U.S. Pat. No. 6,394,090 to Chen, and U.S. Pat. No. 4,873,972 to Magidson et al.
To provide a filtering face-piece respirator that has a permanent cup-shaped configuration, the mask body is typically provided with a molded shaping layer. Molded shaping layers have been made from thermally bonded fibers or open-work filamentary meshes, which are molded into the cup-shaped configuration—see, for example, U.S. Pat. No. 4,850,347 to Skov, U.S. Pat. No. 4,807,619 to Dyrud et al., U.S. Pat. No. 4,536,440 to Berg, and U.S. Pat. No. Des. 285,374 to Huber et al. The shaping layers regularly support a filtering structure that may include an electrically-charged, nonwoven web of microfibers.
To improve wearer comfort, filtering face-piece respirators sometimes have an exhalation valve mounted to the mask body to rapidly purge the wearer's exhaled air from the mask interior; see U.S. Pat. Nos. 7,028,689, 7,188,622, and 7,013,895 to Martin et al. and U.S. Pat. Nos. 7,117,868, 6,854,463, and 6,843,248 to Japuntich et al., and U.S. Pat. No. RE37,974 to Bowers. The quick removal of exhaled air from the mask interior improves wearer comfort.
Exhalation valves have been mounted to respirator mask bodies using a variety of techniques. In some respirators, the valve is welded directly to the various layers that comprise the mask body. In other constructions, the valve seat is clamped to the mask body; see U.S. Pat. Nos. 7,069,931, 7,007,695, 6,959,709, and 6,604,524 to Curran et al. Additionally, a printed patch of adhesive has been used to secure the exhalation valve to the mask body; see U.S. Pat. No. 6,125,849 to Williams et al. In each of these various techniques, the valve is made separately from the mask body and is subsequently attached to the fibrous media and/or open-work filamentary mesh that comprises the mask body.